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Titan

I’ve always been fascinated by Titan. The idea of a moon in our solar system that has an atmosphere has always intrigued me – and it’s the only one in the whole solar system with more than a whiff.

Bigger than Mercury, if it was orbiting the sun Titan would make an impressive planet in its own right. It is the second-largest moon in the solar system, coming in just slightly smaller than Ganymede, and is twice the size and ten times the mass of poor demoted Pluto. Discovered in 1655 by Christiaan Huygens, Titan is an old friend.

Like Venus, until recently its surface has been obscured by cloud. However unlike the hothouse second planet, Titan has an anti-greenhouse effect.

Its distinctive orange colour – pretty familiar now from photographs – is due to a thick organonitrogen haze. In face Titan’s atmosphere is remarkably dense, holding an astounding 7.3 times more per square metre of surface than Earth (1.19 times overall mass). Only its reduced gravity (around 1/7th of earth – 6/7ths of the Moon’s) brings its atmospheric pressure into the highly reasonable range, being roughly one and a half times our own (1.45 atmospheres).

This comparable atmospheric pressure immediately gets me thinking about habitats. You could have fairly lightweight , non-pressurised, structures that maintained a comparable internal pressure to the external environment. Perhaps with an adjusted nitrogen-oxygen mix to bring the oxygen back to 0.21 atmospheres of pressure i.e. 0.21 atm of oxygen pressure with the remainder 1.45-0.21 = 1.24 atm nitrogen, so the actual percent oxygen by volume in the mix is 0.21/1.45 => 15%, yet equivalent to our home-grown partial pressure. Why nitrogen as the balancing gas? There’s heaps of it on Titan!

Titan’s atmosphere comprises about 98.4% nitrogen, with 1.4% methane and the remainder hydrogen. Its thickness also removes the threat of radiation, which is a particular problem for a human presence on the Moon, Mars or asteroids.

Another intriguing reason why Titan is an interesting target for colonisation is the amount of water there. OK. It’s pretty cold: around -179C (-290F). The water is locked up in the planet as solid ice. In fact, it pretty much is Titan ‘rock’. It is estimated that up to half of Titan’s bulk composition is water ice, with the other half rocky material. Volcanoes there spew ‘lava’ composed of water and ammonia.

So the bad news is that you would need some sort of energy source to melt the ice and harvest the oxygen through electrolysis. A nifty little nuclear power plant of the sort proposed for Martian missions would do the trick.

Due to these temperatures, and the light composition of the moon, the ‘methane cycle’ takes the place of the water cycle on Earth. By now descriptions of the vast methane lakes on Titan would be familiar following the descent of the Huygens probe to the surface in January 2005 (wow! Has it really been that long). Based on Cassini data from 2008, Titan bas hundreds of times more liquid hydrocarbons than all known oil and gas reserves on Earth. Now that’s something to consider.

The surface also has many features similar to Earth, despite the difference in composition, such as ‘sand dunes’. Space exploration and settlement advocate Robert Zubrin is keen on Titan, stating “In certain ways, Titan is the most hospitable extraterrestrial world within our solar system for human colonisation”. The nitrogen, methane and ammonia can all be used to produce fertiliser for the biodomes.

Probably the most significant problem (apart from getting there) would be managing the health effects of the low gravity.